Why is negative times negative positive? (VIDEO!)

In grade five I asked my mathematics teacher “Why is negative times negative positive?” The reponse I received was unenlightening to say the least: “It just is!” This made me angry.

In this short video I explain, once and for all, why this peculiar fact is so. [Actually ... that is not quite true! I explain it twice! The first is a way that is acceptable to most, student and teacher alike, and the second is a way that digs a little deeper into the mathematics "behind the scenes" of the first approach, one that satisfies the true mathematician within each of us!]

ON-LINE SHORT COURSES!

QUADRATICS, Permutations and Combinations, EXPLODING DOTS, and more!

Written for educators - and their students too! - this website, slowly growing, takes all the content Tanton has developed in his books, videos, and workshops, and organizes it into short, self-contained, and complete, curriculum units proving that mathematics, at all points of the school curriculum, can be joyous, fresh, innovative, rich, deep-thinking, and devoid of any rote doing! Let's teach generations of students to be self-reliant thinkers, willing to flail and to use their common sense to "nut their way" through challenges, to assess and judge results, and to adjust actions to find success. (Great life skills!)